Amplifier with severed transmission lines

ABSTRACT

A multiple channel amplifier providing both gain and/or phase shift to a microwave signal is formed of a set of transmission lines connected in parallel by means of a power splitter at the input end and a power combiner at the output end of the set of transmission lines. The transmission lines are disposed in a cylindrical array of electrically conducting bars which support amplifying and/or phase shifting elements between the bars and withdraw heat from the amplifying and/or phase shifting elements. The transmission lines may be slotted or severed for directing power flow towards an output terminal of the amplifier. The amplifying and/or phase shifting elements are conveniently mounted on a set of heat sinks to form modules, each of which is readily inserted and detached from the cylindrical array. An enlarged region between adjacent bars serves as the site of a module, the opposed surfaces of the bars and of the heat sink providing the function of a transmission line to conduct power along opposite sides of the module resulting in a push-pull amplifier configuration. Impedance matching is provided by transitions in the bar spacing. The splitter and the combiner may include spider-like structures for coupling the bars to a coaxial line, or a crossed-slot aperture and wedge for coupling the bars to a waveguide.

The invention herein described was made in the course of, or under acontract or subcontract thereunder, with the Department of Defense.

BACKGROUND OF THE INVENTION

Energy in the microwave portion of the electromagnetic spectrum is oftenutilized in communication systems for transmitting data from onelocation to another. While powerful amplifying devices such as travelingwave tubes have been utilized in the past for providing sufficientintensity for transmitting the microwave radiation, the advent of solidstate amplifying devices, operable at microwave frequencies, provides analternative form of amplifying element which is less costly, operates onlower voltages negating the need for high-voltage power supplies, andprovides relatively noise-free amplification over an adequately widebandwidth for use in the communication system.

A problem arises in that the power of present day solid state devices ismuch lower than that of the aforementioned traveling wave tube and othersuch amplifying devices, the lower power precluding the use of a singlesolid state amplifying device in a practical communication system.Amplifiers which combine several solid state amplifying devices in asingle circuit to share the power have had physical structures andcircuit configurations which limit the bandwidth from that which thesolid state devices can supply, and which limit the power dissipation sothat over heating may occur if the amplifying devices are utilized attheir maximum power levels.

SUMMARY OF THE INVENTION

The aforementioned problem is overcome and other advantages are providedby a microwave structure which, in accordance with the invention,accommodates a larger amount of power by distributing the power among aplurality of solid state devices, or semiconductors, such as transistorsand diodes which serve as amplifying or phase shifting elements. Thestructure has multiple parallel branches which support the respectivesemiconductors for processing respective portions of an input signal,the branches being substantially isolated electrically from each otherto insure stability of operation. The branches are formed by a set ofbars, in the form of a cage, wherein the bars are preferably positionedalong a cylindrical surface and parallel to a common axis. Theprocessing involves an amplification, modulation, and/or phase shiftingof the input signal. The microwave structure forms a part of a microwavesystem incorporating a power splitter and a power combiner. The powersplitter has an input port and is connected to one end of the microwavestructure for combining the signal powers in each of the branches toproduce an output signal. The power splitter and power combiner are eachformed of a stepped impedance transformer or tapered waveguide forincreased bandwidth.

The bars are formed of an electrically and thermally conductive materialsuch as copper. The bars are spaced apart and have opposed parallelsurfaces which define individual transmission lines supportingtransverse electromagnetic (TEM) waves wherein the electric fields areconcentrated and made substantially parallel. Individual ones of thebars 30 have sufficiently wide cross sections relative to their lengthsto serve as a conductor of heat for the extraction of heat developedduring the aforementioned signal processing. Individual ones of the barsare recessed or slotted to accomodate the semiconductor amplifyingelements or phase shifting elements which are positioned within thepaths of the electromagnetic waves to accomplish the signal processing.The electric fields of the TEM waves in adjacent waveguides are directedin opposite directions to inhibit radiation of electromagnetic energyboth inwardly and outwardly from the cylindrical array of the bars as istaught with reference to a cylindrical array of wire transmission linesin the U.S. Pat. No. 3,761,834 which issued on Sept. 25, 1973 in thenames of Kenneth W. Dudley, George H. MacMaster and Lawrence J. Nichols.The opposed directions of the electric fields are provided by the powersplitter in a manner to be described. The foregoing constraining of thepropagation of the waves with the transmission lines isolates the signalprocessing in one branch from the signal proprocessing in otherbranches, thereby preventing oscillation and insuring stable operation.To accomplish still further isolation, as may become more desirable asthe gain of the amplifying elements is increased, a resistive shell andouter electrostatic shield, as well as a central slug of resistivematerial, may be employed to further attenuate any coupling ofelectromagnetic energy between the transmission lines as is disclosed inthe aforementioned Dudley patent.

For ease in describing the invention, the use of the term, amplifyingelement, hereinafter will be understood to include complexamplification, namely, the imparting of gain and/or phase shift to theinput signal. Furthermore, since the gain and/or phase imparted bytransistors and diodes is often adjustable by means of electrical biascircuits to admit a modulation of the input signal, it is to beunderstood that the use of the term amplifying element hereinafter alsoincludes the modulation function.

The amplifying element, which may be a transistor or diode circuit, hasa characteristic impedance. The spacing between the bars is preset tomatch the impedance of the transmission line to the characteristicimpedance of the amplifying element. The impedances of the input and theoutput ports are transformed to the impedance of the bar transmissionline by the power splitter and the power combiner, respectively, in amanner to be described.

The power splitter and the power combiner as noted hereinabove, may takeone of two basic forms for connection with a coaxial line or awaveguide. Considering first the description of the power splitter, inthe case wherein the input port is a coaxial line, alternate ones of thebars are coupled to the outer conductor of the coaxial line while theremaining bars are coupled to the inner conductor of the coaxial line.The alternating coupling of the bars to the inner and the outerconductors provides for the periodic reversal of the direction of theelectric fields in the electromagnetic waves propagating between thebars.

For coupling the bars to the inner conductor of the coaxial line, thepower splitter comprises a set of arms which fan out from a centralpoint and may sometimes be referred to hereinafter as an inner spider.The inner spider connects between the bars and the inner conductor, thecentral point being connected to the inner conductor while the arms areconnected to alternate ones of the bars. The arms may fan out graduallyto provide a taper from the inner conductor to the arm or,alternatively, the arms may advance outwardly from the central axis by aseries of steps. A relatively large number of steps or continuous taperresults in a relatively large bandwidth, while a smaller number of stepsresults in a smaller bandwidth for electromagnetic signals propagatingthrough the power splitter.

For coupling the bars to the outer conductor of the coaxial line, acorrespondingly numbered set of arms, which may be referred tohereinafter as an outer spider, is uniformly positioned about theperiphery of the outer conductor. The arms are connected from the outerconductor to alternate ones of the bars. The arms may be tapered orstepped, either to fan in, or to fan out, depending on the relativediameters of the outer conductor and of the cage. A cage of many barswould normally be of much larger diameter than the outer conductor inwhich case the arms of the outer spider fan out from the periphery ofthe outer conductor.

In the case wherein the input port is in the form of a rectangularwaveguide, the power splitter comprises an array of crossed slots in aside wall of the waveguide, and a transition region between the slottedportion of the waveguide and the cage. The transition region includes agenerally conical or hyperboloidal wedge positioned along a central axisof the cage with the apex of the wedge pointing to the crossed-slotarray. The outer wall of the transition region has a frustoconicalshape, the surfaces of the wall and the wedge tapering towards eachother with the minimum spacing occurring adjacent the cage and beingequal to the width of a parallel-plate waveguide. As a result of thecrossed-slot coupling, the transverse electric field of a wavepropagating in the waveguide is converted to an electric field directedcircumferentially around the wedge of the transmission region. Forcoupling the transition region to the transmission lines of the cage,alternate ones of the transmission lines are provided with 180° phaseshifters to provide the aforementioned periodic reversal of direction ofthe electric fields of the TEM waves.

The preceding description of the power splitter also applies to thepower combiner and the coupling of its output port to a coaxial line ora waveguide. The power combiner may be provided with either of theforegoing structures utilized in building the power splitter, since theforegoing structures are reciprocal to the transmission ofelectromagnetic energy.

A feature of the invention is found in the capability of the microwavesystem, composed of the cage of bars in combination with the powersplitter and the power combiner, to accommodate a variety of two- andthree-terminaled solid state devices. Energization of the solid statedevices is accomplished either by use of individual ones of the bars toprovide operating currents and voltages to the solid state devices or,alternatively, by bifurcating the transmission lines around plug-inmodules which contain the solid state devices and are inserted inrecessed portions of the bars. The modules receive the operating currentand voltage from an external source. A further advantage is found in theuse of the module by placing amplifying elements on opposite sidesthereof in a push-pull circuit configuration, this configurationproviding greater isolation between the branches. In the case whereinthe amplifying element is formed of a three-terminated device such asfield effect transistor (FET), isolation of the input and the outputcircuits thereof is readily accomplished by serving a bar between theinput and the output terminals, namely, the drain and the sourceterminals in the case of the FET.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned aspects and other features of the invention areexplained in the following description taken in connection with theaccompanying drawings wherein:

FIG. 1 is a diagrammatic view of a communication system incorporating apower amplifier constructed in accordance with the invention;

FIG. 2 is an isometric view of a set of bars arranged in the form of acircular cage for defining parallel-plate transmission lines for guidingwaves to amplifying elements in the power amplifier of FIG. 1;

FIG. 3 shows an enlarged view of a central portion of a bar of FIG. 2,the view being exploded to show the insertion of a diode into a recessof the bar;

FIG. 4 is a partial view of the assembly of bars of FIG. 2, FIG. 4showing also stepped transition portions appended to the ends of thebars for serving as impedance transitions;

FIG. 5 is an elevation view of the power amplifier of FIG. 1 having fourbars with impedance transition regions appended at the ends thereof;

FIG. 6 is a cross-sectional view of the amplifier of FIG. 5 taken alongthe line 6--6 of FIG. 5;

FIG. 7 is an unfolded view of the amplifier of FIG. 5 taken along theline 7--7 in the cross-sectional view of FIG. 6;

FIG. 8 is a sectional view of the amplifier of FIG. 5 taken along theline 8--8 of FIG. 5;

FIG. 9 is a view of the amplifier of FIG. 5 shown rotated 90° about itslongitudinal axis, the view of FIG. 9 being taken along the line 9--9 ofFIG. 5;

FIG. 9A is a view, similar to that of FIG. 7, of an alternativeembodiment of the amplifier of FIGS. 5-9 wherein the bars are providedwith an additional set of recesses to accommodate a pair of amplifyingelements within each of the transmission lines;

FIG. 10 shows a schematic diagram of a circuit for impressing a voltagebetween an inner and an outer conductor of a coaxial line coupled to thepower amplifier of FIG. 5 whereby the voltage appears between alternateones of the bars to provide a bias voltage to the amplifying elements ofthe power amplifier;

FIG. 11 shows an alternative embodiment of the diode of FIG. 3 whereinthe encapsulation includes end caps for contacting alternate ones of thebars of the amplifier of FIG. 5 whereby the voltage is impressed acrossthe terminals of the diode;

FIG. 12 is a view, similar to that of FIG. 7, of an alternativeembodiment of the amplifier of FIG. 7 wherein alternate ones of the barsare slotted to provide for the excitation of a semiconductor circuit,such as a field effect transistor, having three terminals;

FIG. 13 is a schematic diagram of a circuit, analogous to that of FIG.10, for energizing the semiconductor circuits of an amplifierconstructed in accordance with FIG. 12;

FIG. 14 shows an alternative embodiment of the structure of FIG. 4wherein the recessed regions are enlarged to accept a removable modulecontaining a pair of semiconductor circuits;

FIG. 15 is a cross-sectional view of the module of FIG. 14 taken alongthe lines 15--15 of FIG. 14;

FIG. 16 shows a cross-sectional view of a pair of opposed bars connectedto the center conductors of the coaxial lines in an alternativeembodiment of the amplifier of FIG. 5, the transition sections of thestructure of FIG. 16 being stepped in the radial direction;

FIG. 17 is a plan view of the structure of FIG. 16 taken along the line17--17 of FIG. 16;

FIG. 18 is a cross-sectional view of the structure of FIG. 16 takenalong the line 18--18 of FIG. 17;

FIG. 19 is a cross-sectional view of a pair of opposed bars for theamplifier of FIG. 16, the bars being coupled to the outer conductor ofthe coaxial lines of FIG. 9, the bars terminating in transition sectionswhich are stepped in the radial direction;

FIG. 20 is a plan view of the structure of FIG. 19 taken along the line20--20;

FIG. 21 is a cross-sectional view of the structure of FIG. 19 takenalong the lines 21--21 of FIG. 20;

FIG. 22 shows an elevation view of a further embodiment of the poweramplifier of FIG. 1 wherein the cage of bars is coupled to rectangularwaveguide ports by means of conical waveguides and phase shifterassemblies, a portion of a shield being cut away to expose the cage andvanes connecting from the cage to the phase shifter assemblies;

FIG. 23 shows an elevation view of the conical waveguide of FIG. 22;

FIG. 24 shows an end view of the conical waveguide taken along the line24--24 of FIG. 23, mating flanges thereof being sectioned;

FIG. 25 shows a sectional view of the conical waveguide taken along theline 25--25 of FIG. 23;

FIG. 26 shows an elevation view of the phase shift assembly of FIG. 22;

FIG. 27 shows an end view of the phase shift assembly taken along theline 27--27 of FIG. 26, vanes of the phase shift assembly being shown insection as they continue into a transition section of FIG. 22;

FIG. 28 shows a sectional view of the phase shift assembly taken alongthe line 28--28 of FIG. 27;

FIG. 29 shows a sectional view of the junction between the phase shiftassembly and the conical waveguide of FIG. 22, the phase shift assemblybeing nested in the flanges of the conical waveguide;

FIG. 30 is an elevation view of a vane passing through both phase shiftassemblies, through both transition sections, and through the cage ofFIG. 22;

FIG. 31 is a plan view of the vane of FIG. 30 taken along the line31--31 of FIG. 30;

FIG. 32 is a sectional view of the cage and the transition sectionsabutting the cage taken along the line 32--32 in FIG. 22;

FIG. 33 is a plan view of a rectangular waveguide assembly of FIG. 22including a portion of the conical waveguide to the right of a wedgethereof taken along the line 33--33 through the right-hand conicalwaveguide of FIG. 22;

FIG. 34 is an end view of the rectangular waveguide assembly of FIG. 33taken along the line 34--34 of FIG. 33;

FIG. 35 is a sectional view of the rectangular waveguide assembly ofFIGS. 33 and 34 taken along the line 35--35 in FIG. 22.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, there is seen an exemplary system whichutilizes a power amplifier incorporating the microwave structure of theinvention. More specifically, FIG. 1 shows a communication system 40 fortransmitting a message from one ground station, represented by atransmitting antenna 42, to a second ground station represented by areceiving antenna 44. By way of example, the microwave energytransmitted by the antenna 42 is shown being reflected to the antenna 44by means of a reflector 46 located on top of a mountain.

The message is generated in a signal generator 48 which is coupled via apower amplifier 50 to the antenna 42, and a receiver 52 which is coupledto the antenna 44. Bias circuits 53-53A may be coupled to the input andoutput ports of the amplifier 50 for activation thereof as will bedescribed with reference to FIGS. 10 and 13. By way of example, thegenerator 48 is seen to comprise an oscillator 54 which provides thecarrier at the frequency of the microwave radiation, the generator 48further comprising a modulator 56 coupled between the oscillator 54 andthe amplifier 50 for modulating the carrier with the signal of a voiceapplied to the modulator 56 by a microphone 58. At the receivingstation, the voice is heard by a speaker 60 coupled to the receiver 52.

In accordance with the invention, the power amplifier 50 is providedwith a plurality of amplifying elements 62 disposed in a set oftransmission lines 64 for generating sufficient power to transmit themicrowave radiation along the path from the transmitting antenna 42 tothe reflector 46, and then along the path from the reflector 46 to thereceiving antenna 44. The invention provides for the positioning of thetransmission lines 64 within a unitary structure having the form of acage 66 whereby energy may be coupled thereto via a single inputterminal 68 and coupled therefrom by a single output terminal 70. Thedistribution of power in the signal of the generator 48 among thetransmission lines 64 is accomplished by a power splitter 72. Thecombining of the power from the transmission lines 64 to provide the sumof the powers produced by the amplifying elements 62 at the outputterminal 70 is accomplished by a power combiner 74.

As will be described hereinafter, the dimensions of the transmissionlines 64 are selected to provide a characteristic impedance which ismatched to the impedance of the amplifying elements 62. In the powersplitter 72, the impedances of the respective transmission lines 64 arecombined to provide a combined value of impedance which is matched tothat of the input terminal 68, the combining of the impedances beingaccomplished by a set of impedance transformers 76 which, as will bedescribed hereinafter with reference to FIGS. 4-21, are formed bystepped and/or tapered transitions in the walls of the transmissionlines 64 for the case wherein the input terminal 68 takes the form of acoaxial line. Alternatively, in the case wherein the input terminal 68takes the form of a rectangular waveguide, the impedance transformers 76take the form of a wedge in combination with a crossed-slot aperture inthe wall of the waveguide of the terminal 68 as will be describedhereinafter with reference to FIGS. 22-35. Similar impedancetransformers 78 are utilized in the power combiner 74 for combining theimpedances of the transmission lines 64 to provide a combined impedancewhich is matched to that of the output terminal 70.

Referring now to FIG. 2, the cage 66 of FIG. 1 comprises a set of bars80 which are positioned about a cylindrical surface and are spaced apartwith their opposed surfaces serving as the walls of the transmissionlines 64 which were referred to earlier in FIG. 1. In the preferredembodiment of the invention, the bars 80 are positioned about a rightcircular cylinder. By way of example, the transmission lines 64 areprovided with a ceramic dielectric material, such as alumina, it beingunderstood that an air dielectric may be utilized in lieu of the ceramicas will be seen in the ensuing figures. Amplifying elements 62, whichwill be seen in FIG. 3 as exemplary diodes operating in the avalanchemode, are positioned within respective ones of the transmission lines bymeans of recesses within the bars 80. The bars 80 are fabricated from anelectrically and thermally conducting material such as copper. Theresulting waves in the transmission lines 64 have the form of TEM waves,the waves being indicated diagrammatically in FIG. 2.

A feature of the invention is the orientation of the electric fields ofthe waves in opposite directions in adjacent ones of the transmissionlines 64 to inhibit radiation from the cage 66 which, in the absence ofthe opposed field configuration, would act as a radiator ofelectromagnetic energy. In addition, the microwave energy is inhibitedfrom radiating inwardly into the central portion of the cage 66.Thereby, a signal amplified by one of the elements 62, is not coupled toanother of the elements 62. It is noted that with a large number of thebars 80, the distance across a diameter of the cylindrical surface ofthe cage 66 is much greater than a wavelength of the microwave radiationin vacuum, the diameter being equal to still more wavelengths when thecage is provided with a core 82 of dielectric material.

An electrically conducting shield 84, such as a copper cylinder, may beplaced around the cage 66 to further inhibit the radiation of microwaveenergy from the cage 66. The core 82 may be impregnated with absorptivematerial such as carbon particles for absorbing microwave energy, and acoating 86 of such material may be applied to the inner surface of theshield 84, for absorbing microwave energy. Thereby, the absorptivematerial still further attenuates any coupling of radiation from oneamplifying element 62 to another of the amplifying elements 62. In anexperimental model which was built of only four bars and which utilizedamplifying elements 62 having a relatively low gain, on the order of afew dB (decibels) as will be described with reference to FIG. 5, it hasbeen found that satisfactory operation of the invention was obtainedwithout the use of the absorbing material of the core 82 and the coating86. However, it is suggested that with amplifying elements 62 supplyingsubstantially greater gain than that of the foregoing model, for example20 dB, the absorptive material would advantageously be employed,particularly, in view of the relatively large difference in magnitudesof electric fields at the input and the output terminals of theamplifying elements 62.

Referring also to FIG. 3, the amplifying element 62 is seen to comprisea diode 88 enclosed within an encapsulating module having terminals 90shown schematically coupled via wires 92 to a source 94 of bias voltagewhich sets the operating point of the diodes 88. Also seen in FIG. 3 isa recess 96 within the side of a bar 80 into which an end of the modularamplifying element 62 is secured.

It is noted that the structure of the cage 66 is reciprocal to thepropagation of the electromagnetic radiation. Accordingly, in the FIGS.1 and 2, as well as in the ensuing figures, the input energy will beassumed to be incident upon the cage 66 at the left-hand end thereof,while the output energy will be assumed to exit from the right-hand endof the cage 66.

Referring also to FIG. 4, there is seen a set of the transmission lines64, formed by a set of the bars 80. The transmission lines 64 are seento be jointed to the impedance transformers 76 which are formed bytransitions 98 appended to the ends of respective ones of the bars 80.The transitions 98 may be tapered or stepped, a stepped embodiment beingshown in FIG. 4. A long transition region 98 comprising numerous steps100, or a gradual taper as will be seen hereinafter, provides arelatively wide bandwidth for signals propagating through the cage 66,while a shorter transition 98 comprising fewer steps 100 results in anarrower bandwidth to signals propagating through the cage 66. Toprovide the largest bandwidth for a given number of steps, the sizes ofthe steps 100 have been selected to provide a sequence of impedanceincrements which vary from step to step in accordance with binomialcoefficients, the design of such a sequence of impedances beingexplained in an article appearing in the journal Microwaves on page 48et seq., published by Hayden Publishing Co. in August 1975. As is wellknown, the impedance presented by the parallel-bars of the transmissionline 64 to a TEM wave having its electric vector directed from one wallto the opposite wall increases with increasing spacing between thewalls. Accordingly, the transitions 98 of adjacent ones of the bars 80produce an increasing spacing between side walls of the transmissionlines 64 resulting in an enlarging of the characteristic impedance ofthe waveguide 64. The transitions 98 in combination with the spacingtherebetween which accomplish the foregoing enlarging of the impedanceare shown in FIG. 4 as the impedance transformers 76. The microwavedesign considerations used in the building of the invention as furtherexplained in the book Microwave Filters, Impedance Matching Networks,and Coupling Structures by G. Mathaei, L. Young, and E. Jones at pages267, 281 and 295, published by McGraw Hill Book Company in 1964. It isnoted that the cross-sectional area of a bar 80 and the minimumcross-sectional area of a transition 98 are sufficiently large relativeto the length of a bar 80 and its transition 98 to enable the bar 80 andits transition 98 to serve as a conductor of heat for withdrawing heatfrom the amplifying elements 62 contiguous to the bar 80. Thereby, theamplifying elements 62 are maintained at their proper operatingtemperature since any excess heat developed during the amplifyingprocess is removed by the bars 80.

In constructing the cage 66 of FIG. 2 and the transitions 98 of FIG. 4,it is noted that the lengths of the steps 100, as measured along theaxis of the cage 66, are each equal to an odd number of quarterwavelengths at the center frequency of the bandwidth of the radiation tobe propagated along the cage 66. In a preferred embodiment of theinvention, the steps 100 are provided with a length of one-quarterwavelength. The shield 84 shown covering the cage 66 in FIG. 2 may beextended to cover also the transitions 98 of FIG. 4. The inner surfaceof the shield 84 and its coating 86 are spaced apart from the outercylindrical surface of the cage 66 and from the outer surfaces of thetransitions 98 so as to permit propagation of the TEM waves along thetransmission lines 64 without interference from the shield 84.

Referring now to FIGS. 5-9, there is shown the structural features ofthe power amplifier 50 which were previously described diagrammaticallyin FIG. 1. In the building of the power amplifier 50 of FIGS. 5-9, fourbars such as the bars 80 of FIG. 2 were utilized, the bars beingidentified in FIGS. 5-9 by the legends 80A, 80B, 80C and 80D.Transitions, such as the transitions 98 of FIG. 4, are located at bothends of the bars 80A-D, the transitions being correspondingly identifiedin the FIGS. 5-9 by the legends 98A-D. Transmission lines are formed inthe spaces between the bars 80A-D in a manner similar to that disclosedwith reference to the transmission lines 64 of FIG. 2; however, thetransmission lines of the FIGS. 5-9, which are identified by the legend64A, utilize an air dielectric instead of the ceramic dielectric of FIG.2. The steps 100 each have a length of one-quarter wavelength as isindicated in the drawing of FIG. 7. The amplifying elements 62 arepositioned within recesses of the bars 80A-D to be oriented across thewaveguides as was taught in FIG. 2. However, in lieu of excitation ofthe diodes of the amplifying elements 62 by means of independentlycoupled sources 94 of voltage, as was described with reference to FIG.2, the amplifying elements 62A are to be energized by currents coupledthereto via the bars 80A-D in a manner to be described hereinafter withreference to FIGS. 10-11.

The input and output terminals 68 and 70 of FIG. 1 have been constructedin the form of exemplary coaxial lines 68A and 70A in the embodiment ofFIGS. 5-9. Each of the coaxial lines 68A and 70A comprise an outerconductor 102 and an inner conductor 104. The coaxial lines 68A and 70Aare shown as having an outer diameter which is less than the diameter ofthe cage of the bars 80A-D. Accordingly, the ends of the transitions 98Aand 98C are connected via posts 106 to the outer conductors 102 forsupporting the bars 80A and 80C in their respective positions. Thealternate bars 80B and 80D are supported in their respective positionsby means of posts 108 connected between the inner conductors 104 and therespective ends of the transitions 98B and 98D. The operation of theposts 106 and 108 is in accordance with the operation of a similar setof posts in the transitions shown in the aforementioned Dudley patent.The transitions 98A-D in combination with their respective posts 106 and108 provide the functions of the impedance transformers 76 of FIG. 1 tomatch the impedances of the amplifying elements 62A to the impedance ofthe coaxial lines 68A and 70A. A TEM wave traveling along the coaxialline 68A has its electric field directed transversely in the radialdirection between the inner conductor 104 and the outer conductor 102.In view of the alternating connections of the bars 80A-D to theconductors 102 and 104, the TEM wave produces the alternatingarrangement of the electric field in the TE waves between the bars 80A-Das was described previously with reference to FIG. 2. For example, withreference to FIG. 9, it is seen that an electric vector directed fromthe inner conductor 104 to the outer conductor 102 will, uponpropagation along the transmission line 64A, be directed away from thebar 80B towards the bars 80A and 80C.

Referring also to FIG. 9A, there is seen an alternative embodiment ofthe invention which differs from that of FIGS. 5-9 in that, in FIG. 9A,a pair of amplifying elements 62A are located within each of thewaveguides 64A as compared to the single elements 62A of FIG. 7. Thepair of amplifying elements 62A are spaced apart by a distance ofone-quarter wavelength (λ/4). The embodiment of FIG. 9A provides anadvantage over that of FIG. 7 by a more efficient use of the powerproduced by the amplifying elements 62A. In the embodiment of FIG. 7,the power produced by an amplifying element 62A propagates in twodirections, both toward the input terminal and toward the outputterminal. The portion of the power propagating towards the inputterminal is absorbed within the signal generator 48 and the bias circuit53, and thus does not appear at the output terminal of the poweramplifier of FIG. 7. The quarter wavelength spacing of FIG. 9A providesa phasing between the radiated signals of the two amplifying elements62A in a transmission line 64A such that the radiated signals addconstructively in the forward propagation direction (toward the right),but cancel in the reverse propagation direction (toward the left), sothat substantially all of the radiated power is presented to the outputterminal of the power amplifier of FIG. 9A. Additional amplifyingelements (not shown) may be added at quarter wavelength spacings to morecompletely direct the radiated power of the amplifying elements towardthe output terminal.

Referring also to FIGS. 10 and 11, the amplifying element 62A is seen tocomprise a pair of end caps 110 which are coupled to the terminals ofthe diode 88 in lieu of the terminals 90 of FIG. 3. The end caps 110 arefabricated of an electrically conducting material such as copper andprovide for a direct electrical coupling between the terminals of thediode 88 and a pair of the bars such as the bars 80B and 80C. Thereby,upon applying a bias voltage or current via the bias circuit 53 of FIG.10, the impression of an electric field between the inner conductor 104and the outer conductor 102 results in a difference of potentialappearing between the aforementioned bars 80B and 80C. For example, ifthe inner conductor 104 is made positive relative to the outer conductor102, then the bar 80B becomes positive relative to the bar 80A and alsorelative to the bar 80C. Accordingly, the amplifying element 62A on oneside of the bar 80B would be oriented with its anode coupled to the bar80B and its cathode coupled to the bar 80A, while the amplifying element62A on the other side of the bar 80B would be oriented with its anodecoupled to the bar 80D while its cathode is coupled to the bar 80C. Thesignal generator 48, previously seen in FIG. 1, is coupled via acapacitor 112 of the bias circuit 53 to the coaxial line 68A, a choke114 preventing leakage of the microwave energy of the generator 48 toother parts of the bias circuit 53.

The bias circuit 53 further comprises resistors 117-118, a potentiometer120 and a voltage source represented as a pair of batteries 121-122which are connected at a common terminal to ground 124 and to the outerconductor 102 of the coaxial line 68A. The batteries 121-122 areconnected in series, with the potentiometer 120 being connected acrossthe serial combination of the batteries 121-122. The resistor 118 isconnected to the sliding contact of the potentiometer 120 for selectingboth a magnitude of voltage and the positive or negative sense of thevoltage. The resistor 118 is preferably of a large value as compared tothe resistance of the diode 88 of the amplifying element 62A forsupplying a substantially constant value of current to the diode 88 asthe diode 88 enters the avalanche mode for producing amplification ofthe microwave signal in the power amplifier 50. The resistor 117 servesto match the impedance of the generator 48 and the bias circuit 53 tothat of the coaxial line 68A for a maximum transfer of signal power fromthe generator 48 to the power amplifier 50.

Referring now to FIG. 12, there is seen an unfolded view of analternative embodiment of the amplifier of FIG. 7, the alternativeembodiment of FIG. 12 being identified by the legend 50A. The amplifier50A differs from the amplifier 50 of FIG. 7 in that the bars 80B and 80Dof FIG. 7 are severed in FIG. 12, the severed bars of FIG. 12 beingidentified by the legends 80B' and 80D'. The resulting severs, shown asspaces 126 in the bars 80' and 80D', provide breaks in the walls of thetransmission lines 64A so that a microwave signal of increased amplitudeproduced at the output terminal of an amplifying element is propagatedto the right towards the output terminal of the amplifier 50A withouthaving any significant propagation towards the left to the inputterminal of the amplifier 50A. The amplifier 50A of FIG. 12 demonstratesthe use of a three-terminal amplifying element 62B, such as amplifyingelement being an exemplary FET having the terminals source, drain, andgate identified in the Figure by the legends S, D, and G.

With respect to the withdrawal of heat from the operation of theamplifying element 62B, the terminal of the amplifying element 62Bdissipating the most heat, the drain in the case of an FET, ispositioned in contact with the bar 80A or 80C to facilitate thewithdrawal of the heat. The heat is readily withdrawn via the bars 80Aand 80C as they are connected to the outer conductors 102. The threeterminals G, D and S include metal contacts for making electricalconnection respectively between the left portion of the bar 80B' or80D', the bar 80A or 80C, and the right portion of the bar 80B' or 80D'.The spaces 126, in addition to the aforementioned splitting of the bars80B' and 80D' for directing the amplified microwave power, also permitthe seperate energization of the two portions of the bars 80B' and 80D'to provide separate bias voltages between the gain and source terminals,and between the drain and source terminals as will be described withreference to FIG. 13.

Referring now to FIG. 13, the signal generator 48 is seen to be coupledvia the bias circuit 53 to the amplifier 50A in the manner previouslydescribed in FIG. 10 with reference to the amplifier 50. In addition, asecond bias circuit 53, is similarly coupled to the coaxial line 70A forproviding a difference of potential between the drain and sourceterminals of the amplifying elements 62B. Since the right and leftportions of the amplifier 50A portrayed in FIG. 12 having the same form,the previous description with respect to the bias circuit 53 of FIG. 10applies also to the bias circuit 53A, the components of which functionin a manner analogous to that of the corresponding components of thebias circuit 53.

Referring now to FIGS. 14-15, there is seen a set of bars 128 which arearranged in the same arrangement as the bars 80 of FIG. 4 but havelarger recesses identified by the legend 96A. Each of the bars 128 isterminated by the transitions 98 as is the case with the bars 80 of FIG.4. The structure of FIGS. 14-15 represents an alternative embodiment forconstructing a cage of bars, the structure of FIGS. 14 and 15 differingfrom that of FIG. 4 in that the recesses 96A permit the deployment ofremovable modules such as the module 130.

As seen in the cross-sectional view of FIG. 15, the module 130 comprisesa pair of semiconductor circuits 132, such as FET circuits, positionedon opposite sides of an electrically and thermally conducting block 134,such as a copper block. The bars 128 are severed to provide spaces 126Afor isolating the input and the output terminals of the FET circuits.The sides of the block 134, in cooperation with the sides of therecesses 96A form a bifurcated transmission line wherein a pair ofbranch transmission lines 136 branch off from the transmission line 64Aand couple microwave energy to each of the circuits 132. Thetransmission lines 136 may be formed of alumina or other dielectricmaterial which is readily formed for the fabrication of the module 130.The spacing between the walls of the transmission line 64A is selectedto match the impedance presented by the pair of transmission lines 136to facilitate the splitting of the microwave power among the twotransmission lines 136 and the recombination of the microwave powerafter amplification by the circuits 132. While the transmission lines64A having the air dielectric have been shown in FIG. 15, it isunderstood that the module 130 may be utilized with the transmissionline 64 having the ceramic dielectric. External power for exciting thecircuits 132 is provided by terminals 140 coupled via leads 142 to thecircuits 132 in a manner analogous to that shown previously withreference to the terminals 90 of FIG. 3. It is also noted that all sidesof the copper block 134 of a module 130 are at the same potential, withthe drain terminals of the two circuits 132 being coupled thereto. Thus,the polarities of the FET's are oppositely directed, as are the electricfields of the TEM waves relative to the block 134, to permitenergization of the two circuits 132 of a module 130 in a push-pullconfiguration permitting increased gain and providing isolation betweenthe signals of the respective modules 130. The block 134 serves as anelectrostatic shield between the circuits 132, and also serves as a heatsink for extracting heat dissipated by the circuits 132 during theiroperation. In view of the protrusion of the module 130 outside thecylindrical surface upon which the bars 128 are mounted, the module 130is readily cooled by air which may be blown past the module 130 wherebythe heat produced by the circuits 132 is dissipated.

Referring now to FIGS. 16-18, there is seen an alternate configurationfor the transitions appended to the ends of the bars 80B and 80D of FIG.5, a transition 144 being utilized in the FIGS. 16-18 in lieu of thetransition 98 of FIG. 5 for supporting the bars 80B and 80D upon theinner conductors 104. The transitions 144 are seen to have a differentform from the transitions 98 in that the transitions 144 are stepped inthe radial direction R and tapered in the circumferential direction, θ,the R and θ coordinates being seen in both FIGS. 6 and 18. In contrast,the transition 98 is stepped in the circumferential direction andsupported by posts 108 in the radial direction. The length of the stepsof the transitions 144 are equal to one-quarter wavelength as is thecase with the transitions 98.

Referring now to FIGS. 19-21, there are seen the bars 80A and 80C ofFIG. 9 connected to the outer conductor 102 via an alternative form oftransition identified by the legend 145. The transition 145 is utilizedin lieu of the transition 98 with its posts 106 of FIG. 9. Thetransition 145 differs from the transition 98 in that the transition 145is stepped in the radial direction and tapered in the circumferentialdirection. Thus it is seen that the transitions 144-145 of FIGS. 16-21may be utilized for supporting the bars 80A-D, 80B', 80D' and 128 inlieu of the transitions 98 of FIGS. 5-9, 12 and 14. It is also notedthat the stepping of the transition 144 need be provided only on theouter surface of the transition 144, while the stepping of thetransition 145 need be provided only on the inner surface thereof. Thetransitions 144-145 are preferred for situations wherein the cage ofbars has a diameter much larger than the diameter of the outer conductor102 since the transitions 144-145 avoid the occurrence of the suddenchange in diameter brought on by the use of the posts 106 and 108 and,therefore increase the bandwidth of the amplifier 50 of FIGS. 1 and 5.

Referring now to FIG. 22, there is seen an amplifier 50B which is analternative embodiment of the power amplifier 50 of FIG. 1. Theamplifier 50B is preferable to the amplifier 50A of FIGS. 5-9 for theamplification of microwave signals of higher frequency such as X-bandand higher. As is known in the design of coaxial cables, the diameter ofthe inner conductor is reduced at the higher frequencies with the resultthat the inner conductor can no longer carry high currents withoutexcessive resistive loss. Accordingly, for high power applications, awaveguide is preferred to a coaxial line. The amplifier 50B incorporatesthe cage 66 of FIG. 1 and has the input terminal 68 and the outputterminal 70 fabricated of rectangular waveguide assemblies 150.

The waveguide assemblies 150 are coupled via circular waveguides 152 toconical waveguides 154 which will be described with reference to FIGS.23-25. The conical waveguides 154 are coupled via phase shift assemblies156, which will be described with reference to FIGS. 26-29, totransition sections 158 which will be described with reference to FIGS.30-32 and which, in turn, are coupled to the cage 66. A shield 160 ofmicrowave absorbing material, such as that utilized in the core 82 ofFIG. 2, may be provided as shown in FIG. 22, the shield 160 beingsupported by the assemblies 156 and having an inner surface which isspaced apart from the cage 66 and the transition sections 158. Thetransition sections 158 are formed of open, parallel-walled,transmission lines similar to that of the cage 66 while closedwaveguides, to be described hereinafter, are utilized within the phaseshift assemblies 156.

Referring now to FIGS. 23-25, the conical waveguide 154 is seen tocomprise a central wedge 162 positioned along the central axis of theouter wall 164 of the waveguide 154. Both the wedge 162 and the wall 164are formed of an electrically conducting material, such as copper. Boththe wedge 162 and the wall 164 are provided with flanges 167-168 formating with the phase shift assembly 156 as will be described in FIG.29. The waveguide 154 provides for a distribution of power appliedthereto from the waveguide 152 uniformly around the wedge 162 so that atransverse component of the electric field is found to circulate aroundthe wedge 162.

Referring now to FIGS. 26-29, the phase shift assembly 156 is seen tocomprise an inner cylindrical wall 170 and an outer cylindrical wall 172which are fabricated of an electrically conducting material such ascopper. The walls 170 and 172 are provided with longitudinal recessesfor receiving the edges of vanes 174 which divide the space between theinner and outer walls 170 and 172 into waveguides 176 having asubstantially rectangular cross-sectional shape. Alternate ones of thewaveguides 176 are provided with phase shifters 178 having the form ofwedges of a ceramic material such as alumina, the phase shifters 178being affixed to the short walls of the waveguides 176 and having agradual taper for increased bandwidth. The cross-sectional dimensions ofthe waveguides 176 are sufficiently large so as to insure that thebandwidth of the microwave signal lies well above the cut-off frequencyof the waveguides 176. Since the parallel-walled transmission lines 64or 64A of the cage 66 are not so restricted as to the frequency ofpropagation of microwave energy, the transmission lines 64 or 64A may beprovided with cross-sectional dimensions that are smaller than those ofthe waveguides 176, such an arrangement being shown in FIG. 22. Thephase shifter assembly 156 mates with the conical waveguide 154 as isseen in FIG. 29 wherein the inner conductor 170 is nested within theflange 167 and the outer conductor 172 is nested within the flange 168.

The transverse electric field coupled via the conical waveguide 154 tothe phase shift assembly 156 is incident upon each of the waveguides 176of the phase shifter assembly 156. At the moment of incidence, theelectric field has the same sense in each of the waveguides 176. Afterthe microwave energy has propagated through each of the waveguides 176,the waves propagating through the alternate ones of the waveguides 176containing the phase shifters 178 experience a phase shift of 180°relative to waves propagating in the other waveguides 176 so that, asthe waves reach the waveguides of the cage 66 of FIG. 22, the sense ofthe transverse electric field is reversed periodically from waveguide towaveguide in the manner described previously with reference to FIG. 2.

Referring also to FIGS. 30-32, the vanes 174 are seen to extend from onephase shift assembly 156 to the other phase shift assembly 156. The midportion of a vane 174 is seen to decrease in the R direction at thecenter portion of the vane 174 and is seen to increase in the θdimension at the middle of the vane 174. Since the middle portion of avane 174 serves as a member of a transmission line of the cage 66, asseen in FIGS. 22 and 32, the reduced dimension along the R coordinateand the increased dimension along the θ coordinate provides for asmaller cross-sectional dimension to the waveguides of the cage 66. Atthe ends of the vanes 174, the enlarged dimension along the R coordinateand the decreased dimension along the θ coordinate provide for thelarger cross-sectional dimensions of the waveguides of the phase shiftassemblies 156. In addition to the shield 160, shown in FIG. 32 alongthe outer perimeter of the assembly of the vanes 174, a second shield180 of the same microwave absorbing material as the shield 160, isadvantageously placed along the interior perimeter of the assembly ofthe vanes 174 for he absorption of any microwave energy which mayradiate from the transmission lines formed by the vanes 174. The taperedportions of each vane 174, at the right and left sides of the centralportion, provide the transition sections 158 wherein the impedance ofthe waveguides of the phase shift assemblies 156 is converted to theimpedance of the parallel-plate transmission lines of the cage 66. Inlieu of the smooth taper of the vane 174 which maximizes the bandwidthof the amplifier 50B, the vanes 174 may comprise a series of steps (astaught with the transition 98) to provide an impedance transition whichis of slightly reduced bandwidth but more easily fabricated.

Referring now to FIGS. 33-35, the waveguide assembly 150 comprises arectangular waveguide 182 which branches into two waveguides 183 and184. The branching takes place in a transition region 186 wherein theshort wall of the waveguide 182 is enlarged to form the two waveguides183-184 each of which has cross-sectional dimensions equal to that ofthe waveguide 182. A vane 188 separates the waveguide 183 from thewaveguide 184. A set of four slots 190 are arranged in the configurationof a crossed-slot aperture as viewed along the axis of the circularwaveguide 152, two of the slots 190 being located in a short wall of thewaveguide 183 while the other two slots 190 are located in a short wallof the waveguide 184. A bifurcated plunger 192 having a first portion inthe waveguide 183 and a second portion in the waveguide 184 ispositioned by the turning of a knob 194 having a threaded stem foradjusting the physical and electrical lengths of the waveguides 183-184to tune the waveguide assembly 150 for coupling a maximum power betweenthe waveguide 182 and the circular waveguide 152. A set of four tappedholes 196 are located around the end of the waveguide 182 for securing afurther waveguide or probe assembly (not shown) for coupling power, forexample, between the power amplifier 50 and the antenna 42 of FIG. 1.

In summary, it is seen that the amplifying elements 62 or circuits 132may be supported directly by the bars of the transmission lines 64-64Aas shown in FIGS. 2, 5, 12 or supported by the modules as shown in FIGS.14-15, and in either case the transmission lines are coupled to anexternal circuit by the impedance transformers 76-78 of FIG. 1 which maytake either one of the forms shown in FIGS. 4, 5, 16, 19 and 22. Thetransmission lines are preferably severed as shown in FIGS. 12 and 14for the use of transistor amplifying elements to insure that the outputpower is directed toward the output terminal. In the case of diodeamplifying elements, the severing of the transmission lines is notrequired, and adequate directivity for the flow of power can be attainedby the use of a series of two, or more, diodes arranged in an array asshown in FIG. 9A. In the case of the modules of FIG. 14, diodes may beutilized in lieu of the transistors in which case the diodes would beencapsulated for support within the module as is done with thetransistors, the diodes being oriented transversely of the transmissionlines as shown in FIG. 3.

It is understood that the above-described embodiments of the inventionare illustrative only and that modification thereof may occur to thoseskilled in the art. Accordingly, it is desired that this invention isnot to be limited to the embodiments disclosed herein but is to belimited only as defined by the appended claims.

What is claimed is:
 1. A system for processing radiant energycomprising:a set of parallel bars, said bars being spaced apart toprovided passages therebetween, said bars being configured to provide apair of opposed parallel sides to each of said passages to admit thepropagation of radiation along said passages; means for couplingradiation to said passage, said coupling means being adapted foralternating the sense of a transverse field of said radiation betweenadjacent ones of said passages; and wherein said bars are severed toprovide isolation between terminals of an electrical circuit coupled tosaid bars.
 2. A system according to claim 1 wherein said bars arepositioned along a cylindrical surface.
 3. A system according to claim 2further comprising a set of said electrical circuits, said circuitsbeing amplifying elements wherein individual ones of said amplifyingelements are positioned within said passages by slots in said bars.
 4. Asystem according to claim 3 wherein said amplifying elements have aplurality of terminals for electrically energizing said amplifyingelements, said terminals being electrically connected to respective onesof a plurality of said bars, said bars being constructed of electricallyconductive material for conducting electric power to said terminals forenergizing said amplyfying elements.
 5. A system according to claim 1wherein the sides of a plurality of said bars are slotted for receivingsaid electrical circuit, said circuit being an amplifying element.
 6. Asystem according to claim 1 wherein said coupling means comprisestransition structures coupled to said bars, said transition structuresintroducing enlargements in the spacing between neighboring ones of saidbars.
 7. A system according to claim 6 wherein said transitionstructures include a plurality of steps having a length of an integralnumber of one-quarter wavelength of the nominal frequency of saidradiation.
 8. A system according to claim 6 wherein said transitionstructures are laterally displaced from a terminal for said radiation byarms of a set of radially directed arms.
 9. A system according to claim6 wherein said transition structures include inner and outerconically-shaped waveguide walls and a set of waveguides arrangedcircumferentially around said inner conical waveguide wall andcontacting said outer waveguide wall.
 10. A system according to claim 9further comprising phase shifting elements located in alternate ones ofsaid circumferentially arranged waveguides of said transitionstructures.
 11. A matched channel amplifier structure comprising:a setof longitudinal members disposed parallel to a common axis and arrangedalong a cylindrical surface; opposed sides of adjacent ones of saidmembers being parallel and defining a set of parallel-walledtransmission lines which admit the propagation of radiation; alternateones of said members being coupled at their respective ends to a heatdissipating element for the dissipation of heat from said members intoan external atmosphere; means coupled to the termini of respective onesof said transmission lines for combining the power of said radiation inone of said transmission lines with the power of said radiation in asecond of said transmission lines; and recessed regions in the sidewallsof a plurality of said members communicating with said transmissionlines for supporting amplifying elements in respective ones of saidwaveguides.